In orthodontic treatment, a patient's teeth are moved from an initial to a final position using any of a variety of appliances. An appliance exerts force on the teeth by which one or more of them are moved or held in place, as appropriate to the stage of treatment.
The mechanism of the orthodontic movement, as a result of one to one correlation between the tooth position and the appliance generation is that the teeth are “squeezed” into the new configuration and held in place, allowing the teeth sufficient time to adapt to the new position, before the process is repeated again as the teeth move progressively along the various treatment stages of a treatment plan.
In the one to one correlation between the current treatment state and the subsequent target or n+1 treatment stage, the adaptation of the dental appliance may include interactions between the plastic and the tooth geometry which is suboptimal for achieving n+1 tooth position, and is typically not factored into the correlation. This may be the case in particular for larger distances of tooth movement, where the amount of appliance distortion may lead to stretch and stress in the appliance whereby some areas of the aligner are not in close contact with the teeth in critical and/or desirable areas. As a result, the teeth may not be moveable to the desired target position. Moreover, the opposite effect may also exist, where the teeth may be in contact in areas which are counterproductive to reaching the desired or target position.
In addition, the dental attachments are used primarily for changing the geometry of the tooth crown to assure better grip of the dental appliance such as an aligner in the direction of the desired movement. Generally, the attachments operate to provide “bumps” or “undercuts” on the vertical surface of the tooth which otherwise would be difficult for the dental appliance to grip.
Existing approaches to achieve the desired movement of the tooth include fabrication of dental appliances from the planned next or n+1 position and placed over the teeth during the current or n position of the treatment stage. Typically, it is assumed that the forces and torques generated by the deformation of the dental appliance or portions thereof (resulting from the difference in the teeth position used for the dental appliance fabrication and the position of the teeth it has been positioned over) will cause the teeth to move into the planned next position in the treatment stage.
In practice, however, the generated forces and torques may not be oriented in the direction of the intended tooth movement, whether or not dental attachments are used in the treatment. Further, the current tooth movement may be programmed or configured only for the tooth crown, and not factoring into the root of the tooth or other anatomical structures. The root of the tooth or other anatomical structures may hinder the crown movement and render the center of resistance down in the tooth bone socket. Generally, the undesirable torque to the center of resistance as a result of the force on the tooth crown may not be easily counter balanced. Moreover, as the teeth move during the course of the treatment, the deformation of the dental appliance diminishes, rendering the applied forces to diminish as well.